This invention is related to oil extended ethylene alpha-olefin or ethylene alpha-olefin and diene copolymers. Ethylene alpha-olefin elastomers, particularly ethylene-propylene-diene terpolymers (EPDM), are recognized as excellent general-purpose elastomers that are useful in a variety of applications. It is generally known that small amounts of diene units in EPDM introduce unsaturation and thus facilitate crosslinking/vulcanization of the polymer chains. The vulcanization reaction involves using one or more curing agents that causes two or more elastomeric polymer chains to cross-link chemically. The vulcanization takes place during the post-polymerization process, such as in an extruder.
The molecular weight of the ethylene elastomer is also known to affect the elastomeric properties of the composition. While higher molecular weight elastomers provide improved rubber elastic properties, the inherent high viscosity of high molecular weight ethylene elastomer creates difficulties in processability, including mixing and compounding steps. Therefore, it is common for rubber manufacturers to add process/extender oil after the polymerization, but prior to vulcanization of the ethylene elastomer to form an oil-extended rubber or elastomer product. The amount of extender oil added depends on the molecular weight of the ethylene elastomer and end-use applications. For EPDM, extender oil is typically added to reduce the apparent viscosity to a Mooney viscosity of about 100 mu or below. For high resilience applications, EPDM typically contains from about 50 to about 125 phr (parts per hundred parts resin) extender oil. Oil extension is also a feature demanded by industrial mixing operations to facilitate fast processing and mixing of EPDM, as the oil facilitates the lubrication, wetting, and proper dispersion of the ingredients.
As stated, in oil-extended EPDM manufacturing processes, the extender oil is typically blended with the ethylene copolymer post polymerization reactor. Oil introduction takes place after the reactor but before the removal of volatiles, for instance before a steam stripper. To achieve good mixing, the extender oil is often blended with the ethylene copolymer when the ethylene copolymer is still dissolved or suspended in the reaction media coming from the polymerization reactor. However, oil extension adds an extra step to manufacturing and leaves the choice of extender oil to the rubber manufacturer, not the fabricators of the rubber articles. Additional hardware is also necessary to carry out post-reactor oil addition. Accordingly, there is a need for a process of in-situ oil production in the polymerization reactor, thereby eliminating the need of additional hardware in the post polymerization reactor for oil addition. The inventors have discovered a process to incorporate in-situ oil to produce olefin oligomers and ethylene alpha-olefin elastomers. Specifically, the olefin oligomers have vinyl chain ends so that some of the oligomers are incorporated into ethylene alpha-olefin elastomer chains to form branched polymer structures. The remaining un-incorporated oligomers serve as extender oil to the elastomers. The inventors have also discovered that this process allows for controlling the levels of branching to eliminate the formation of a gelled product.